Intake/exhaust valve seal structures of internal combustion engines of related art made up of circular, elliptical or oval valves and valve seats, and intake/exhaust valves for internal combustion engines of related art with circular or elliptical head parts, are known from for example JP-UM-A-62-183007. The content of JP-UM-A-62-183007 will be discussed with reference to FIG. 8 and FIG. 9.
A manufacturing method of an intake/exhaust valve for an internal combustion engine of related art in which an onion-shaped part of an intermediate blank is pressed with a punch to form a head part of a final product shape is known from for example JP-A-2000-117386. The content of JP-A-2000-117386 will be discussed below with reference to FIGS. 10A and 10B.
In FIG. 8, an elliptical or oval intake valve seat 102 and a circular exhaust valve seat 103 are provided in a cylinder head body 101.
In FIG. 9, an intake valve 105 is fitted seatably in the intake valve seat 102 and an exhaust valve 106 is fitted seatably in the exhaust valve seat 103.
In FIG. 8 and FIG. 9, for example the sealing surface created by the circular exhaust valve seat 103 and the circular exhaust valve 106 lies on a conical surface. When the sealing surface is made a conical surface like this, the female taper surface on the exhaust valve seat 103 side forming the sealing surface and the male taper surface on the exhaust valve 106 side forming the sealing surface can each be formed with high accuracy and their gastightness made high, and the female taper surface and the male taper surface can be machined relatively easily.
However, when the exhaust valve seat 103 is circular, the area of the ceiling of the combustion chamber occupied by the exhaust valve seat 103 cannot be made large enough, and intake/exhaust efficiency is impaired. When an oval shape is adopted, as in the case of the intake valve seat 102, although the area of the opening of the intake valve seat 102 can be made larger than when it is circular, the space between this valve seat and the adjacent valve seat is still not being utilized effectively. If this space can be utilized effectively, while improvement of the gastightness of the sealing surface of the intake valve seat 102 and the intake valve 105 and improvement of the machinability of the intake valve seat 102 and the intake valve 105 are achieved, the area of the opening increases, intake/exhaust efficiency rises, the amount of air taken in increases (the amount of mixture also increases), and the output of the internal combustion engine improves.
FIG. 10A and FIG. 10B illustrate a method for manufacturing an intake/exhaust valve of an internal combustion engine. In FIG. 10A, an intermediate blank 114 made up of an onion-shaped part 111 and a stem part 112 extending integrally from this onion-shaped part 111 are pressed with a punch 117 into a die 116.
FIG. 10B shows the onion-shaped part 111 (see FIG. 10A) having been molded into a head part 121 to complete a valve 122, which is a finished product.
When the elliptical intake valve 105 and the circular exhaust valve 106 shown in FIG. 8 and FIG. 9 are employed, when the intake valve seat 102 and the exhaust valve seat 103 are disposed in the inner wall of the combustion chamber, a large space remains between these adjacent valve seats in the inner wall. If this space can be used more effectively, the profiles of the intake valve seat 102 and the exhaust valve seat 103 can be made large, along with this the profiles of the intake valve 105 and the exhaust valve 106 can be made large, and the intake/exhaust resistance of when the intake valve 105 and the exhaust valve 106 open can be reduced. One way to take advantage of the space is for example to make the profiles of the valve seats and valves a complex shape other than circular, elliptical or oval.
In FIG. 10A and FIG. 10B, to mold the profile of the head part 121 of the valve 122 to a complex shape, it is necessary to form a complex female shape on the die 116. In particular, to raise seal quality, the valve face surface that forms the sealing surface together with the valve seat must be formed to a high accuracy, and to form a valve face surface on the die 116 to a complex shape and to a high accuracy is difficult. Also, the cost of manufacturing an intake/exhaust valve with a complex shape is desired to be low.
Accordingly, means have been awaited for achieving improved gastightness of the sealing surface created by the valve seat surface and the valve face surface and improved machinability of the valve seat surface and the valve face surface while raising the intake/exhaust efficiency of the internal combustion engine, manufacturing an intake/exhaust valve with a non-circular complex shape particularly other than elliptical or oval easily and with high accuracy, and reducing cost.